Campaigners are calling for a halt to plans for a Nato radar station on the island of Madeira amidst fears it could harm Europe's most endangered bird.

The proposed site of the station is already designated as a Special Protection Area under European law - and the Zino's petrel is classified as "critically endangered".

This is a test case of whether national security can outweigh the potential survival of an entire species

Helder Costa, Portuguese Society for the Study of Birds

The station would be built near the summit of the Pico do Areeiro on the Portuguese-administered island.

Conservation group Birdlife International has written to Nato to ask them to make a full assessment of the likely impact of the development on the bird.

There are only an estimated 20 to 30 breeding pairs left, which makes the petrel Europe's most threatened breeding bird.

The Portuguese Ministry of Defence claims its own assessment shows no evidence that the building will interfere with the bird population.

'No margin for error'

Canan Orhun, head of Birdlife International's European Division, said: "The Zino's petrel is on the verge of extinction. We see no margin for error in this case.

"Given the lack of information about its potential impacts, and according to the precautionary principle, construction of the radar must either be suspended or a new site found for it.

Helder Costa, the president of the Portuguese Society for the Study of Birds, added: "There are already too many threats to this bird's survival. This radar station could be the proverbial 'straw that breaks the camel's back'.

"This is a test case of whether national security can outweigh the potential survival of an entire species."

The Zino's petrel is not particularly adept at surviving.

During the past 10 years, breeding success has amounted to an average of fewer than one fledgling bird per nest per year.

Experts are worried that there could be further disturbance of the breeding pairs during construction work.